Electrical Mystery

U

ursus

Well-known member
Today, I went to start my coupe after replacing the generator. Normally The engine fires up after a couple seconds but today it would fire up but crap out after a few seconds. After several attempts with the same result, I did some trouble shooting, finding 6.3 volts at every point along the way including the BAT side of the cutout. The timing was tested and found to be spot on.

While turning the ignition off and on during the troubleshooting I observed the ammeter jump a bit to the discharge side, as normal. After not finding anything amiss I attempted to start the engine but noticed that ammeter now failed to jump a bit as normal when turning on the key. Turning on the lights failed to move the ammeter needle at all.

I would appreciate any thoughts about this issue. Thanks much!
 
Do you have the fuse that sits on top of the starter near the starter switch? I you do then check it with an ohm meter and make sure the contacts are good (shinny and tight). Otherwise there can be an intermittent connection anywhere in the circuit from the battery to the distributor including the ammeter, ignition switch and any connection points. It can also be loose or corroded battery terminals and ground connections. Or a bad battery. You just have to go through the entire system with your multimeter to check for a problem.
 
I'd run that "voltage drop test" a second time and see where you're losing the voltage. Remember the voltage has to be "on" to do the test. Like the head lights would need to be turned on to test every connection in the lighting circuit. You're not testing for available voltage; you're testing for a voltage loss. Try the meter between the battery post and cable, then between two cable ends on the same cable. There are some YouTube videos on voltage drop testing. That's how we found open's in circuits on the modern cars
 
I had an intermittent pop out switch causing a similar problem, replaced it with a new but non stock type and fixed it.Good luck.
 
I have no fuse in the system, a modern switch (no pop-out), and I did excite the cutout to polarize it. What baffles me is that the ammeter somehow went south and doesn't register anything. Maybe I should take the ammeter out to the system and see if it will start?
 
ursus said:
I have no fuse in the system, a modern switch (no pop-out), and I did excite the cutout to polarize it. What baffles me is that the ammeter somehow went south and doesn't register anything. Maybe I should take the ammeter out to the system and see if it will start?
Click to expand...

FUN FACT:
You can "take the ammeter out of the system" by temporarily connecting a wire between the 2 brass wing nuts on the front of the terminal box.

This can be very handy of you have an ammeter problem on the road and want to bypass it to get home.

I hope this helps you find your problem.
 
Jim/GA said:
FUN FACT:
You can "take the ammeter out of the system" by temporarily connecting a wire between the 2 brass wing nuts on the front of the terminal box.

This can be very handy of you have an ammeter problem on the road and want to bypass it to get home.

I hope this helps you find your problem.
Click to expand...

Following the advice of Jim/GA, I bypassed the ammeter circuit and the old girl started up as normal. Turned out that the repo ammeter had fried which resulted in an open in the ignition circuit. The repo ammeter had only hex nuts for securing the wire leads, unlike the original Ford unit that had bakelite knobs for the same purpose. The hex nut arrangement probably made contact with the dash sheet metal and that ended its useful life. Lesson learned!
 
ursus said:
Following the advice of Jim/GA, I bypassed the ammeter circuit and the old girl started up as normal. Turned out that the repo ammeter had fried which resulted in an open in the ignition circuit. The repo ammeter had only hex nuts for securing the wire leads, unlike the original Ford unit that had bakelite knobs for the same purpose. The hex nut arrangement probably made contact with the dash sheet metal and that ended its useful life. Lesson learned!
Click to expand...

Ammeters usually burn up because of heat generated when current flows through them and you don't have a really good connection. This could be a bad internal connection or a bad connection on the back where the wires connect.

Before you install the replacement ammeter, watch this video on how to open up a reproduction ammeter and improve the electrical connections inside.

https://www.youtube.com/watch?v=n85WuQachEQ

When connecting wires to the back, make sure the nuts are tight and don't loosen up as you manipulate the instrument panel into position. Insulated nuts are a good idea, but are not usually the source of the ammeter burning up.

I'm glad you were able to find the problem with the help of my little Tech Tip.
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